1. Field of the Invention
The present invention relates to a copper (Cu) electroplating method and more particularly, a method for forming low resistively copper (Cu) electron lines.
2. Discussion of the Related Art
In general, a copper (Cu) conductor line is used for signal lines of a liquid crystal display (LCD) device or plasma display panels (PDPS). As the size of flat panel display devices increase, electrical resistively of conductive lines used in the devices decreased. Accordingly, copper (Cu) has been commonly used as the material with which to form the conductive lines.
FIG. 1 is a perspective view of a liquid crystal display (LCD) device according to the related art. In FIG. 1, a liquid crystal panel has upper and lower substrates 5 and 22, and liquid crystal material layer 11 interposed therebetween. The upper substrate 5 includes a color filter 8 having a black matrix 6 and sub-color filters 7, and a common electrode 9 formed on the color filter 8. The lower substrate 22 includes a pixel region “P,” a pixel electrode 17 within the pixel region “P,” and a plurality of gate lines 12 and a plurality of data lines 24 electrically connected to a thin film transistor “T.” The lower substrate 22 is commonly referred to as an array substrate, and a plurality of thin film transistors “T” are arranged in a matrix arrangement. The pixel region “P” is defined by a crossing of the gate and data lines 12 and 24. The pixel electrode 17, which is formed within the pixel region “P,” is formed of a transparent conductive material having a high transmissibility, such as indium tin oxide (ITO). The liquid crystal display (LCD) device displays images using the thin film transistor “T” and the pixel electrode 17. The gate line 12 delivers a pulse voltage for driving a gate electrode of the thin film transistor “T,” and the data line 24 delivers a signal voltage for driving a source electrode of the thin film transistor “T.”
The liquid crystal panel 51 is driven by electron-optical effects of liquid crystal material 11. For example, the liquid crystal material 11 has a dielectric constant anisotropy and spontaneous polarization properties. If a voltage is applied to the liquid crystal material 11, the liquid crystal molecules form a dipole due to their spontaneous polarization. Thus, an alignment direction of the liquid crystal molecules changes according to a direction of the applied voltage. Accordingly, light modulation occurs due to the change of optical properties depending on the alignment direction of the liquid crystal molecules. Images can be displayed by interrupting or transmitting light by the light modulation.
The data line 24 is commonly formed of a conductive metal material having superior thermal stability in order to prevent formation of hillocks, such as chromium (Cr), molybdenum (Mo) and tantalum (Ta). The gate and data lines 12 and 24 are commonly formed by depositing a metal material on the array substrate 22 using a physical vapor deposition method (PVD), such as a sputtering, and then by wet etching or dry etching the deposited metal material. However, while the metal materials have superior thermal stability, its high specific resistance induces a signal delay as the size of the image display device increases. Accordingly, materials that do not form the hillock and have low specific resistances have been developed.
Copper and aluminum are commonly used materials for forming conductive lines because of their low specific resistances. However, using aluminum can be problematic due to generation of hillocks. Accordingly, aluminum alloys have been developed to overcome hillock generation, but the aluminum alloys have high specific resistances. However, copper requires additional processes for forming a diffusion barrier since copper easily diffuses into silicon, such as silicon oxide (SiO2) and silicon substrates. In addition, the diffusion barrier increases the specific resistance of copper because of its own high specific resistance overshadows any advantage that copper offers as the material for conductive lines.